Means for regulating balance between currents in associated circuits



April 6, 1937.- r w. A. MUELLER 7 MEANS FOR 'REGULATING BALANCE BETWEEN CURRENTS IN ASSOCIATED cmcum's v Fiied Aug. 11, 1933 1 2 Sheets-Sheet 1 FILM EPROD w a) 14 PIE. 2. t f LIGHT FILM l FILM EZZ MPLIFIE AMPLIF/EQ AMPLIFIER b ,2 AMPLIFIER I 'ALVE u F/LM PEPPODUCE MPLIF/EQ ISOLATING LI AMPLIFIED 3 1 k) FILM S Armour: g PECT/HEI? INVENTOR WILLIAM A. MUELLER BY ATTORNEY w. A. MUELLER 2,075,861

IN ASSOCIATED CIRCUITS April 6, 1937.

MEANS FOR REGULATING BALANCE BETWEEN CURRENTS Filed Aug. 11, 1933- 2 Sheets-SheetZ 0 335 LZMQQDU kDnibo QMEIUUQ 2 3 lNPUT T0 QECT/F/El? (voups A.CJ

2s- 50 as 4o and 4u u4 mK uukku INVENTDFQ WILLIAM A. MUELLER 20 DIALOGUE LEVEL (05) ATTORNEY Patented Apr. 6, 1937 UNITED STATES MEANS FOR REGULATING BALANCE BE- TWEEN CURREN TS CIRCUITS IN ASSOCIATED William A. Mueller, Hollywood, Calif., as'signor to United Research C orporation, Long Island City, N. Y., a corporation of Delaware Application August 11, 1933, Serial No. 684,669

2 Claims.

The invention relates to method and means for regulating balance between currents in associated circuits, and particularly to improvements in the background regulator sound recording arrangement of my Patent No. 1,888,467, issued Nov. 22, 1932 for Sound recording. Fig. 2 of that patent discloses an arrangement wherein the background or sound effects currents are varied in volume in accordance with the dialogue. Experience has shown that if the volume or level of the current in the sound effects circuit is varied too rapidly by the current in the dialogue circuit, the change would be noticeable on reproducing 7 the resulting sound record. An object of the invention is to prevent this change in level from being noticeable. This is accomplished by delaying for a short time, such as a fraction of a second, the control of the sound effects currents by the dialogue currents.

A further object of the invention is to prevent the amplifier in the sound effects circuit from giving rise to noise currents at times when currents from that amplifier are suppressed by the dialogue currents. This is accomplished by emplaying a, suppressor grid variable MU type tube in the amplifier for the sound effects currents.

Another object of the invention is to prevent door slams, heavy footsteps and other low frequency sounds on the dialogue track from varying the level of the effects. This is accomplished by employing in the dialogue circuit an amplifier which has a reduced or low gain at low frequencies, whereby substantially the whole controlling eifect of the sound effects currents by the dialogue currents is due to the dialogue currents and not to extraneous low frequency sounds.

For further details of the invention, reference may be made to the drawings, wherein: Fig. 1 is a diagrammatic view of a preferred circuit.

Fig. 2 is a schematic view of a rerecording or duping channel embodying the circuit of Fig. 1.

Fig. 3 is a curve illustrating a preferred rectifier characteristic.

Fig. 4 is a curve illustrating the relation between the level of dialogue and level of effects for a 13 db. reduction in the effects level.

The general circuit arrangement is illustrated in Fig. 2, which circuit corresponds in arrangement and function to that of Fig. 2 of the abovementioned patent, except that the dialogue amplifier l is provided at its input circuit with a transformer 2 having a split primary winding 3 with a /z m. f. condenser 4 connected in the middle thereof in order to provide reduced transmission below a frequency of 250. cycles and normal transmission thereabove, in order to keep out of the dialogue circuit extraneous low frequency sounds, such as door slams or heavy footsteps.

Generally speaking the arrangement and function of the circuit of Fig. 1 herein corresponds to the arrangement and function of the circuit of Fig. 1 of the above-mentioned patent. The circuit of Fig. 1 herein differs from and contains improvements over the circuit of Fig. 1 of the patent in the following respects:

The amplifier I4 is known as a suppressor grid variable MU tube type 58 and has the advantage pointed out above that when the biasing poten-' tial at potentiometer 26 is high enough to reduce the amplification of this tube to a negligible quantity, this tube remains substantially noiseless and, in fact, it is noiseless also at normal values of grid bias. The suppressor grid 28 is connected to the cathode lead 29.

In order to delay the effect of the dialogue currents on the sound effects currents, the rectifier I1 is provided in series in its output circuit with a choke coil 4'! of about 232 h., with a shunt condenser 52 of about 2 m. f. and with a shunt condenser 53 of about 2 m. 1. As pointed out above, the choke coil 41 and condensers 52 and 53 constitute a delay circuit for delaying the control of amplifier M by rectifier ll, whereby for normal amounts of reduction of current in amplifier I 4, the variation in level is not noticeable.

The purpose of resistor 5| in the output circuit of rectifier I1 is to flatten out the rectifier characteristic as shown in Fig. 3, whereby the rectified current output will be proportional to the input voltage to the rectifier only up to some value, such as 2 volts, and thereafter a further increase in the voltage on the rectifier will not result in any substantial increase in the rectified output current. Consequently, a softspoken voice for the dialogue circuit, corresponding to low input, depresses the amplified current for the sound eifects circuit a desired amount, and a louder dialogue sound does not needlessly depress the sound effects currents further.

As the amplifier l4 overloads at a comparatively low level, in order to prevent harmonic distortion, this amplifier I4 is installed in the circuit at the point of lowest amplification, that is as the first amplifier in the series.

The amount that the variable gain amplifier l4 reduces the level of the sound effects currents,

40 54, Fig. 2, is placed on the mixers table is controlled by the setting of the potentiometer 26 which may be calibrated in 2 db. steps. The current through the amplifier M can be reduced by the rectified current as much as db., although 8 or 10 db. is all that has been found necessary. The relation between the level of the sound effects currents and the level of the dialogue currents for a reduction of about 13 db. is illustrated in Fig. 4.

The potentiometer 54 of Fig. 2 is placed at the" the-mixer can control mixers position so that the input level to the rectifier and therefore use as much or as little background regulation as desired or cut it out entirely. Also at the mixers position is placed a meter 40 in shunt to a resistance 48 in the plate circuit of rectifier H, whereby the mixer can read the intensity of the rectified current. v

The invention therefore provides an improved automatic balance regulator whereby the volume of the sound effects is varied automatically and simultaneously in accordance with the dialogue level. The volume of the sound effects is reduced as the dialogue is being spoken, the amount of reduction being in proportion to the level of the dialogue, and the speed of reduction being delayed so that the reduction is not noticeable to the ear. When the dialogue ceases the sound effects are restored to their normal volume.

The entire equipment may be terminated'on jacks as will be readily understood so that it can be patched into the circuit when it is required and removed when it is not necessary. It is very flexible as any number of effects sound tracks can be controlled by the dialogue, music or any other sound. By merely turning the dial on the potentiometer 26, the mixer can vary over wide limits the maximum amount the effects or music are depressed. A second control, the potentiometer so that the mixer can use as much or as little background regulation as he desires, or cut it out entirely. Also, the extension meter 49 is bridged off the rectifier and is installed at the mixers table so that the mixer can better control the action of the device.

The background regulator herein described gives an improved sound record with the dialogue perfectly understandable at all times, the background music loud and full, and effects which are loud enough to contribute to the realism of the picture photographed in synchronism with the sound thusrecorded.

Having thus described the invention, what is claimed as new and desired to secure by Letters Patent, is:

1. A sound recording circuit comprising the combination of a plurality of audio frequency circuits, a common output circuit therefor, an amplifier in one of said audio frequency circuits, a rectifier connected to said amplifier and also connected to supply rectified current to another of said audio frequency circuits for controlling the volume of audio frequency currents in said other circuit, and means included in the circuit interconnecting said rectifier and said last mentioned audio frequency circuit, said means comprising a circuit having a series inductance of approximately 232 henries, a condenser shunting said circuit on one side of said inductance of approximately 2 m. f. and a condenser shunting said circuit on the other side of said inductance of approximately 2 m. f., said inductance and condensers providing a definite amount of delay in the controlling action of the rectified currents from said rectifier.

2. A sound recording circuit in accordance with claim 1 in which said amplifier has connected in the input thereof a high pass filter for decreasing the effect of low frequencies on the control circuit, said filter comprising a condenser connected in series in the primary winding of an input transformer of said amplifier.

WILLIAM A. MUELLER.

CERTIFICATE OF CORBECTIOIL Patent No. 2,075,861. April 6, 1937.

WILLIAM A MUELLER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1,

first column, line 1, strike out the words "method and" page 2, first 7 column, line 15, for "4-0" read 49; and that the said Letters Patent should be read with these corrections th erein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 8th day of June, A. D. 1937.

Henry Van Arsdale (Seal) Acting Commissioner of Patents. 7 

